My annecdata is that I spent two years eating a healthy vegetarian diet (to contrast with french fry vegetarians) and my digestive tract never adapted. I switched back to eating plenty of lean meat (mostly chicken and fish) and the plumbing almost instantly began working properly.

The added benefit is that my diet is much higher in protein and lower in carbs, which definitely has helped me build and maintain muscle and reduce dad bod.

Again, just annecdata, but maybe individuals have differing nutritional profiles that work best for them?